As magnetic head devices, there are a longitudinal recording (in-plane recording) type head device which performs a magnetic field parallel to a recording head surface to perform information recording, and a perpendicular magnetic recording type head device which applies to a magnetic field perpendicular to a recording medium surface to perform information recording, the perpendicular magnetic recording head device of which is considered prevailing in consideration of future higher-density recording.
The perpendicular magnetic recording head device has a laminated structure formed by providing a return path layer on a main magnetic pole layer with a nonmagnetic insulating layer interposed between the main magnetic pole layer and the return path layer, on the surface (medium-facing surface) thereof facing a recording medium. The main magnetic pole layer and the return path layer are electrically connected to each other on the deeper side in the height direction than the medium-facing surface. Moreover, coil layers for applying a recording magnetic field to the main magnetic pole layer and the return path layer are buried in the nonmagnetic insulating layer. In a magnetic head device that has such a configuration, a recording magnetic field is induced between the main magnetic pole layer and the return path layer by energizing the coil layers. This recording magnetic field perpendicularly enter a hard film of the recording medium from the medium-facing surface of the main magnetic pole layer, and returns to the return-path layer through a soft film of the recording medium. This allows information to be recorded in a region that faces the main magnetic pole layer in the recording medium (see Japanese Unexamined Patent Application Publication No. 2005-122831) (corresponding to US Publication No. 2005/0083608 A1).
In recent years, a so-called shielded pole structure is suggested in which the spacing (gap spacing) between a main magnetic pole layer and a return path layer in a surface that faces a recording medium is narrowed to about 50 nm so that magnetic recording that has little leakage can be realized by controlling divergence of a magnetic field directed to the return path layer from the main magnetic pole layer. In a perpendicular magnetic recording head device that has the shielded pole structure, the dimension (throat height) of the return path layer in a depth direction in addition to the above gap spacing becomes an important parameter for controlling a recording magnetic field. It is thus necessary to set this throat height properly.
However, in the structure described in Japanese Unexamined Patent Application Publication No. 2005-122831, if the throat height is set low, the facing area between a main magnetic pole layer 1 and a return path layer 2 becomes small as shown in FIG. 10A, and consequently a magnetic flux (φx) leaks easily toward a recording medium M from the main magnetic pole layer 1. For this reason, a magnetic flux returning to the return path layer from the main magnetic pole layer diverges easily, and thus it becomes difficult to sufficiently increase magnetic field gradient (sharpness in the change of magnetic field intensity in a recording region). As a result, excellent recording performance cannot be exhibited. On the other hand, if the throat height is set high, the facing surface between the main magnetic pole layer 1 and the return path layer 2 becomes large as shown in FIG. 10B. Thus, a magnetic flux (φb) flows easily towards the return path layer from the main magnetic pole layer 1. For this reason, the magnetic field gradient rises, but the magnetic flux (φx) directed to the recording medium M from the main magnetic pole layer 1 decreases, and thus recording magnetic field intensity may fall. As a result, information recording cannot be performed well.